The described aspects relate generally to wireless communication systems. More particularly, the described aspects relate to prioritizing time critical data for transmission during a power-limited state in DC-HSUPA operation.
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. Furthermore, UMTS supports multiple radio access bearer (multi-RAB) capability, which allows simultaneous network communication with a user equipment (UE) over two or more radio access bearers. Therefore, in an aspect, multi-RAB functionality in UMTS allows for a UE to concurrently transmit and receive packet-switched (PS) and circuit-switched (CS) data.
A UE may operate in Dual Cell (or Dual Carrier) High Speed Uplink Packet Access (DC-HSUPA), or simply Dual Carrier Uplink (UL), mode in W-CDMA. As such, a UE operating in DC-HSUPA may be able to transmit data on two uplink (UL) carriers: a primary uplink carrier and a secondary uplink carrier. If such a UE is in a power-limited state (e.g., the UE is using its maximum power such that it does not have enough power available to build a transport block having even the smallest size possible), the UE can rely on a minimum set Enhanced Dedicated Channel (E-DCH) Transport Format Combination Indicator (E-TFCI), which also may be referred to as a MIN SET E-TFCI (which is described in the 3GPP specifications), provided and/or specified by the network to transmit critical data even if the UE is in a power-limited state. E-TFCI may inform a receiver (e.g., a UE) of a transport block size coded on Enhanced Dedicated Physical Data Channels (E-DPDCH). From this information, the receiver may determine how many E-DPDCHs are transmitted in parallel and a spreading factor. As such, information provided by the MIN SET E-TFCI may be a predefined transport block size (e.g., a predefined amount of data) that may be used by a UE to transmit data during a power-limited state.
In some instances, there may be non-scheduled Signaling Radio Bearer (SRB) data, which includes time critical information, stored along with scheduled Packet Switched (PS) data available in a Layer 2 (L2) buffer. Layer 2 includes a Medium Access Control (MAC) layer that performs E-TFCI selection on an UL carrier.
Generally, when a UE operating in DC-HSUPA is in a power-limited state, which may be determined by Layer 2, E-TFCI selection may first be performed for transmission via a secondary UL carrier, followed by E-TFCI selection for transmission via a primary UL carrier. In the case of the non-scheduled, time critical SRB data waiting in the L2 buffer (along with scheduled PS data), and when the UE is in a power-limited state, there may not be enough power headroom for transmission of the non-scheduled, time critical SRB data on the primary UL carrier during the current transmission time interval (TTI). As such, any attempted transmission of the non-scheduled, time critical SRB data may fail in the current TTI, and potentially later TTIs as well, causing a delay in transmission of the time critical data.
As such, improvements in transmission of time critical data when a UE is in a power-limited state may be desired.